The present invention relates to gas turbine engine casings, particularly gas turbine engine fan casings and turbine casings, more particularly to an improved blade containment assembly for use within or forming a part of the gas turbine engine casing.
Turbofan gas turbine engines for powering aircraft conventionally comprise a core engine, which drives a fan. The fan comprises a number of radially extending fan blades mounted on a fan rotor enclosed by a generally cylindrical fan casing. The core engine comprises one or more turbines, each one of which comprises a number of radially extending turbine blades enclosed by a cylindrical, or frustoconical, casing.
There is a remote possibility that with such engines that part, or all, of a fan blade, or a turbine blade, could become detached from the remainder of the fan or turbine. In the case of a fan blade becoming detached this may occur as the result of, for example, the turbofan gas turbine engine ingesting a bird or other foreign object.
The use of containment rings for turbofan gas turbine engine casings is well known. It is known to provide generally cylindrical, or frustoconical, relatively thick metallic containment rings. It is also known to provide generally cylindrical, or frustoconical, locally thickened, isogrid, metallic containment rings. Furthermore it is known to provide strong fibrous material wound around relatively thin metallic casings or around the above mentioned containment casings. In the event that a blade becomes detached it passes through the casing and is contained by the fibrous material.
However, the relatively thick containment casings are relatively heavy, the relatively thin casings enclosed by the fibrous material are lighter but are more expensive to manufacture. The relatively thick casings with fibrous material are both heavier and more expensive to manufacture.
It is known to provide a hard metallic liner within the thin metallic casing having a fibrous material wound around the think metallic casing. The hard metallic liner is positioned upstream of the fan blades and comprises a radially inwardly extending flange arranged to deflect detached fan blades radially outwardly so that the fan blades pass through the casing to be contained by the fibrous material.
Accordingly the present invention seeks to provide a novel gas turbine engine casing which overcomes the above mentioned problems.
Accordingly the present invention provides a gas turbine engine rotor blade containment assembly comprising a generally cylindrical, or frustoconical, first metal casing, the first metal casing having different axially spaced gas turbine engine rotor blade containment regions, at least one generally cylindrical, or frustoconical, second metal casing, the at least one second metal casing surrounding and abutting the first metal casing, the first metal casing being relatively hard and tough to contain a gas turbine engine rotor blade, the at least one second metal casing being relatively soft and lightweight to stiffen the first metal casing in a gas turbine engine rotor blade containment region.
Preferably the at least one second metal casing is arranged coaxially with the first metal casing.
Preferably there are a plurality of second metal casings, the second metal casings being axially spaced along the first metal casing to support the first metal casing in different gas turbine engine rotor blade containment regions.
Preferably the at least one second metal casing is in a plane containing the rotor blades of the gas turbine engine.
At least one second metal casings may be axially downstream of the plane containing the rotor blades of the gas turbine engine.
One of the second metal casings is axially upstream of the plane containing the rotor blades of the gas turbine engine.
Preferably the at least one second metal casing has ribs and/or blind apertures.
Preferably one or more continuous layers of a strong fibrous material are wound around the at least one second metal casing and first metal casing.
Preferably the first metal casing comprises a steel alloy or a nickel alloy.
Preferably the second metal casing comprises aluminium or an aluminium alloy.
Preferably an acoustic lining is provided within the first metal casing.
The present invention also provides a gas turbine engine comprising a rotor carrying a plurality of rotor blades, a rotor blade containment assembly comprising a generally cylindrical, or frustoconical, first metal casing, the first metal casing being arranged coaxially around the rotor and rotor blades, the first metal casing having different axially spaced gas turbine engine rotor blade containment regions, at least one generally cylindrical, or frustoconical, second metal casing, the at least one second metal casing surrounding and abutting the first metal casing, the first metal casing being relatively hard and tough to contain a gas turbine engine rotor blade, the at least one second metal casing being relatively soft and lightweight to stiffen the first metal casing in a gas turbine engine rotor blade containment region.